Field of the Invention
The present invention relates to a power-generating device having a power generator provided with a dynamo coil that generates electricity by capturing the kinetic energy produced when a rotor is rotated by a rotating weight or the like, and to a clocking device using such a power-generating device.
In recent years, timing devices, such as wristwatches, have been developed with built-in electricity generators that convert the energy generated by the movement of the user's arm into electricity used to drive the stepping motor of the device. As such, timing devices with such built-in electricity generators have eliminated the need to change the battery, which is often a cumbersome process. Furthermore, and more importantly, where the need for a battery is eliminated, the need to dispose of the used, potentially hazardous battery is also eliminated. As a result, the economic and environmental advantages offered by built-in electricity generators make them particularly desirable for use in wristwatches and similar devices.
One example of a conventional portable electronic device is depicted in FIG. 1. Clocking device 401 includes a power-generating device 409 and a rotating weight 411 arranged to turn within a case of clocking device 401. The turning movement of rotating weight 411 is transmitted to a rotor 413 of a dynamo 410 via a wheel train mechanism 412. As rotor 413 rotates, an electromotive voltage is generated in a dynamo coil 415 provided on a stator 414. An alternating current output from dynamo 410 is rectified by a rectifying portion 402 that includes a rectifier diode 402a, and is then charged in a charging portion 404 that includes a large-capacity capacitor 405. Rectifying portion 402 may be a rectifier circuit, such as a full-wave rectifier circuit or a voltage doubling rectifier circuit.
A functioning device 406, such as a timepiece 407, can be operated by utilizing electric power from charging portion 404 of power-generating device 409. Dynamo 410 comprises rotor 413, which may be a disk-shaped, bipolar permanent magnet, and stator 414, which is attached to rotor 413. Rotation of rotor 413 generates an electromotive voltage in dynamo coil 415 of stator 414, which is output from dynamo coil 415 as an alternating current.
In the conventional power-generating device 409 described above, however, when capacitor 405 of charging portion 404 is charged to a certain voltage value, the electromotive voltage generated in dynamo coil 415 cannot be charged in the large-capacity capacitor 405, unless the electromotive charge is greater than a charged voltage value of capacitor 405. Thus, in many cases, kinetic energy caught by rotating weight 411 cannot be converted efficiently into electrical energy.
FIG. 2 shows one example of movement of rotating weight 411 of clocking device 401. Assume now that, as shown in FIG. 2(a), rotating weight 411 is set to lie in a vertical plane, and after being raised to its uppermost position (180 degrees), rotating weight 411 is acted upon by gravity. At this position, when rotating weight 411 is acted upon by gravity, one of two events occurs: (1) rotating weight 411 stops at a position of zero degrees, as shown in FIG. 2(b); or (2) rotating weight 411 overshoots the position of 0 degrees by several degrees or more, as is shown in FIG. 2(c). In the case depicted in FIG. 2(b), all of the potential energy stored in rotating weight 411, when rotating weight 411 is positioned at 180 degrees, is converted into kinetic energy when rotating weight 411 is acted upon by gravity, and is captured as electrical energy, when rotating weight 411 stops at position of 0 degrees (less mechanical losses produced by, for example, by the bearing and wheel train mechanisms of the rotor).
In contrast, in the case depicted in FIG. 2(c), when rotating weight 411 has dropped by the force of gravity and reached the position of 0 degrees, rotating weight 411 still has kinetic energy stored therein and therefore overshoots beyond the position of 0 degrees by several degrees or more. Stated otherwise, at a position of 0 degrees, not all of the kinetic energy is converted into electrical energy, as a part of the kinetic energy remains stored in rotating weight 411. In the case of FIG. 2(c), the overshoot of rotating weight 411 repeats damped oscillation and the weight 411 gradually settles to the position of 0 degree. At this time, the kinetic energy stored in rotating weight 411 has been consumed incrementally by mechanical losses produced by, for example, bearing and wheel train mechanisms of the rotor, and correspondingly the electromotive voltage charged as a result of the induction of voltage into dynamo coil is gradually reduced. Therefore, the kinetic energy stored in rotating weight 411 is in not efficiently converted into electrical energy for charging charging portion 404.
Accordingly, once charging portion 404 is charged to a certain level, it has been conventional that when rotating weight 411 is acted upon by gravity or captures a motion of the user of wrist watch device 401, and the electromotive voltage generated in dynamo coil 415 by such force is so small that it does not exceed the charged voltage of charging portion 404, no attempt is made to store the kinetic energy of rotating weight 411.
Further, as a practical matter, where clocking device 401 is used as a wrist watch, it is rare that a user's wrist motion rotates rotating weight 411 in one direction from its uppermost position as is the case depicted in FIGS. 2(a) and 2(b), because a user's wrist motion is typically a continuous motion. Therefore, as shown in FIG. 2(c), when the charged voltage of charging portion 404 becomes sufficiently high, and the potential difference between the charged voltage and the electromotive voltage generated in dynamo coil 415 is small, a user's wrist motion often causes rotating weight 411 to rotate in the direction of arrow B, opposite to the direction rotating weight 411 rotated initially, as is indicated by arrow A. Thus, where the wrist motion is continuous, the kinetic energy provided to rotating weight 411 is reduced as a result of the canceling effect of the forces depicted by arrows A and B. This makes it difficult to produce electric power by catching the motion of the user's wrist or the like with high efficiency.
On the other hand, when the electromotive voltage generated in dynamo coil 415 is sufficiently larger than the charged potential of charging portion 404, a high charging brake has been applied to rotating weight 411 so as to decrease the speed with which rotating weight 411 rotates. In this case, the kinetic energy caught by rotating weight 411 through one stroke of drop motion can be captured as electrical energy very efficiently. However, the time required for a charging process to be completed is delayed because of the time it takes rotating weight 411 to complete one stroke of drop motion. Further, as is mentioned above, the motion of the user's wrist rarely ceases at the time rotating weight 411 completes one stroke of drop by gravity; to the contrary, the motion is typically a continuous motion. Accordingly, even if a large amount of charge is obtained with one stroke of drop motion of rotating weight 411, the charging time may be so long that the movement of rotating weight 411 which rotates based on wrist motion, would have to be prevented from following the continuous wrist motion to proceed in the same direction for such a long period. Therefore, because rotating weight 411 cannot efficiently catch the kinetic energy of the wrist motion, the efficiency of converting the wrist motion into electrical energy is reduced.
One example of a prior art device is shown in Japanese Unexamined Patent Publication No. 6-300865, which describes an electronic watch having a power-generating device that converts mechanical energy into electrical energy by utilizing the motion of the human body or gravity. In this case, as described above, the weight is moved by the movement of a human body, and that movement is transmitted through a gear train, which in turn moves a magnet of a generator relative to the generator coil. The movement of the magnet is detected to control the amount of load applied to the magnet upon power generation by the power-generating device. Specifically, the reference discloses that the electromotive voltage generated by a dynamo is compared with the charged voltage of a capacitor serving as an electricity accumulating member, and a transistor is provided to connect or disconnect the dynamo coil to the capacitor or load. With the provision of such a transistor switch, when the transistor permits electricity to be conducted (in its closed position), a charging current flows to generate a charging brake applied to the rotating weight, whereas when the transistor does not permit electricity to be conducted (in its open position), no charging current flows and a load, such as a charging brake, is not applied to the rotating weight. Accordingly, the charging efficiency can be improved by properly controlling those two conditions.
When the input motion applied to rotating weight 411 is so small that no electricity can be charged with an ordinary rectifier circuit, the transistor is set open to reduce the load of rotating weight 411, causing rotating weight 411 to freely turn. Conversely, when a large input motion is applied to rotating weight 411, the transistor is set to be closed to allow electricity to be conducted. By controlling the transistor in this manner, when the transistor is open when the input motion is small, the kinetic energy of rotating weight 411 is not used for charging of electricity and no charging brake is applied to rotating weight 411. As such, rotating weight 411 continues in a state of motion with kinetic energy remaining stored therein. A portion of the kinetic energy stored in rotating weight 411, however, is consumed by mechanical losses. Further, the kinetic energy provided to rotating weight 411 upon the continuous motion of the user's wrist is consumed as a result of canceling or offset forces in the directions of the arrows A and B (FIG. 2(c)) when the direction of rotation is changed by the user's motion. Accordingly, even under the above control, when the kinetic energy is small and the electromotive voltage of dynamo coil 415 is not greater than the voltage charged in the capacitor, charging of electricity is ineffective.
Conversely, when an input motion applied to rotating weight 411 is large (and hence would supply a large electromotive voltage), it is also possible to control the transistor to be set in an open position by permitting rotating weight 411 to freely turn without being impeded by a load. In this case, while the transistor permits electricity to be conducted only when a relatively small input motion is applied to rotating weight 411. This control permits the storage of a greater amount of kinetic energy in rotating weight 411, and reduces the charging brake applied to rotating weight 411 when a large amount of charge is charged as electrical energy, because electricity is charged in the capacitor only during the period in which the transistor permits electricity to be conducted. With the above control, however, the amount of charge itself is reduced. Specifically, the large amount of charge that could be obtained when a large input motion is applied to rotating weight 411 is reduced to a level comparable to that achieved with a small input motion of rotating weight 411, because the end of the dynamo coil is kept disconnected from the capacitor during the large input motion. Also, regardless of whether the transistor permits electricity to be conducted, charging of electricity cannot be effected when the electromotive voltage of the dynamo coil is less than the voltage charged in the capacitor. Thus, even when the above-mentioned control is employed, it is difficult to efficiently produce electrical energy for charging the capacitor by converting the kinetic energy of rotating weight 411.
The above explanation is equally applicable to any type of power-generating device where an electromotive voltage is produced in a dynamo coil by catching kinetic energy provided by forces other than a rotating weight, such as a spring or wind. Therefore, despite having the ability to convert the kinetic energy provided by the very user of a portable clocking device, where the device contains a power-generating device that serves as its power supply, electricity is ineffectively charged if the input motion provided is slight. As a result, the clocking device may fail to operate or operate unreliably.
Accordingly, it is desirable to provide a power generating device that overcomes the drawbacks of the prior art.